Automatic document conveying device and image forming apparatus including the same

ABSTRACT

Provided is an automatic document conveying device, including: a document feeding portion that feeds a document from a document stacking tray; a conveying portion that conveys the document which is fed, to a document reading portion; a discharge portion that discharges the document after being read to a discharge tray; a branching guide that switches a conveying path so that a second surface is read after a first surface of the document is read; and a switchback portion including a switchback roller pair for sending the document to the conveying portion again after the conveying path is switched by the branching guide, in which a switch of the conveying path by the branching guide and open/close of a nip of the switchback roller pair are performed in one drive portion.

This application is based upon and claims the benefit of priority fromthe corresponding Japanese Patent Application No. 2010-009464 filed onJan. 19, 2010, the entire contents of which are incorporated herein byreference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an automatic document conveying devicethat conveys a document to a reading position automatically, and animage forming apparatus including the automatic document conveyingdevice.

2. Description of Related Art

As an automatic document conveying device used in a copier, a scanner, afacsimile, etc., there are well-known automatic document conveyingdevices in a form capable of inverting front and back surfaces of adocument so as to read both surfaces of the document. In recent years,along with the downsizing of an image forming apparatus, there is also ademand for the downsizing of the automatic document conveying device aswell as an image forming portion of the image forming apparatus.

FIG. 13 illustrates a related technology of such an automatic documentconveying device. The related technology of the automatic documentconveying device includes a document stacking tray (101), a pickuproller (102), a sheet feeding roller (103), a conveying drum (104), afront reading roller (105) and a back reading roller (106) disposed soas to be in contact with the conveying drum (104), a branching member(107), a lower inversion roller (108), an upper discharge roller (109),an inversion guide (110), and a discharge tray (111) in this order in aconveying direction (direction of an arrow “a”) of a document (D).Further, a document reading position (R) is located below the conveyingdrum (104) between the front reading roller (105) and the back readingroller (106). For convenience of the description, an upper surface ofthe document placed on the document stacking tray (101) is referred toas an A-surface and a lower surface thereof is referred to as aB-surface.

When only the A-surface of the document is read, the A-surface of thedocument (D) supplied by the pickup roller (102) from the documentstacking tray (101) is read at the document reading position (R). Thebranching member (107) is supported so as to be swingable about an axisat its back end. When only the A-surface of the document (D) is read,the branching member (107) is placed at a position indicated by a solidline illustrated in the figure, and the document (D) is discharged tothe discharge tray (111).

When both the surfaces (A-surface and B-surface) of the document areread, after the A-surface of the document (D) conveyed from the documentstacking tray (101) is read at the document reading position (R), thedocument (D) is inverted by the lower inversion roller (108), the upperdischarge roller (109), and the inversion guide (110) due to thepresence of the branching member (107) at a position indicated by adotted line illustrated in the figure. Then, the document (D) isconveyed to the document reading position (R) and the B-surface is read.The document (D) is further inverted again due to the similar operationand discharged to the discharge tray (111).

In the above-mentioned related technology, the number of members such asa conveying roller for use in the automatic document conveying device isreduced by configuring the automatic document conveying device asdescribed above. However, drive sources of the branching member (107)and the lower inversion roller (108) are provided separately, and hencethere is a problem in that spaces are required for setting therespective drive sources. Further, in a case of using an inexpensivesolenoid as a drive source, the noise from the drive source increases,which requires countermeasures against the noise. Consequently, there isalso a problem in that the number of parts increases to increase thenumber of assembly steps, leading to an increase in production cost.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide an automaticdocument conveying device which is capable of reducing a number of drivesources such as a motor, down-sizing of a drive portion, reducing anumber of parts of the drive portion to obtain a simple configuration,and further, capable of suppressing an operation sound to reduce noise,and to provide an image forming apparatus including the automaticdocument conveying device.

An automatic document conveying device according to an aspect of thepresent invention, includes: a document feeding portion that feeds adocument from a document stacking tray; a conveying portion that conveysthe document which is fed, to a document reading portion; a dischargeportion that discharges the document after being read to a dischargetray; a branching guide that switches a conveying path so that a secondsurface is read after a first surface of the document is read; and aswitchback portion including a switchback roller pair for sending thedocument to the conveying portion again after the conveying path isswitched by the branching guide, in which a switch of the conveying pathby the branching guide and open/close of a nip of the switchback rollerpair are performed in one drive portion.

Further features and advantages of the present invention will becomeapparent from the description of embodiment given below.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of an automatic document conveyingdevice according to an embodiment of the present invention.

FIG. 2 is a perspective view illustrating a drive portion of theautomatic document conveying device according to the present invention.

FIG. 3 is a side view illustrating the drive portion of the automaticdocument conveying device according to the present invention.

FIG. 4 is an enlarged perspective view illustrating the drive portion ofthe automatic document conveying device according to the presentinvention.

FIG. 5 is a cross-sectional view of the automatic document conveyingdevice according to the embodiment of the present invention duringsingle-side conveyance.

FIG. 6 is a cross-sectional view of the automatic document conveyingdevice according to the embodiment of the present invention duringdouble-side conveyance.

FIG. 7 is a first operation state diagram of a cam, a branching guide,and a switchback roller pair of the automatic document conveying deviceaccording to the embodiment of the present invention.

FIG. 8 is a second operation state diagram of the cam, the branchingguide, and the switchback roller pair of the automatic documentconveying device according to the embodiment of the present invention.

FIG. 9 is a third operation state diagram of the cam, the branchingguide, and the switchback roller pair of the automatic documentconveying device according to the embodiment of the present invention.

FIG. 10 is a fourth operation state diagram of the cam, the branchingguide, and the switchback roller pair of the automatic documentconveying device according to the embodiment of the present invention.

FIG. 11 is a fifth operation state diagram of the cam, the branchingguide, and the switchback roller pair of the automatic documentconveying device according to the embodiment of the present invention.

FIG. 12 is a sixth operation state diagram of the cam, the branchingguide, and the switchback roller pair of the automatic documentconveying device according to the embodiment of the present invention.

FIG. 13 is a cross-sectional view of an automatic document conveyingdevice of a related technology.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENT

An automatic document conveying device and an image forming apparatusincluding the same according to an embodiment of the present inventionare described in detail with reference to the drawings. The presentinvention is not limited to the embodiment. Further, an intended use,terms, etc. described herein of the present invention are not limitedthereto.

FIG. 1 is a cross-sectional view of the automatic document conveyingdevice according to the embodiment of the present invention. In thefollowing description, the left side of the figure is assumed to be aleading end of the automatic document conveying device and the rightside of the figure is assumed to be a back end thereof.

As illustrated in FIG. 1, an automatic document conveying device (1)includes a document stacking tray (2) on which documents are to beplaced, a document feeding portion (3) which supplies documents stackedon the document stacking tray (2) one by one, a conveying portion (4)which conveys a document fed by the document feeding portion (3) to adocument reading portion (18), a discharge portion (5) which dischargesthe document after being read by the document reading portion (18), abranching guide (6) which switches a conveying path of the document, aswitchback portion (7) which switches back the document to invert frontand back surfaces of the document introduced to the conveying pathswitched by the branching guide (6) and conveys the document to theconveying portion (4) again, and a document discharge tray (8) whichreceives the discharged document.

The document stacking tray (2) is provided above the back end side ofthe automatic document conveying device (1). The document stacking tray(2) is formed in a substantially planar shape, and tilts gently anddownwardly toward the leading end of the automatic document conveyingdevice (1), thereby facilitating the supply of the document to thedocument feeding portion (3). A leading end of the document placed onthe document stacking tray (2) comes into contact with a separation wall(9) formed between the document stacking tray (2) and the documentfeeding portion (3), and passes over the separation wall (9) during thesupply of documents, to thereby supply the documents to the documentfeeding portion (3) one by one. It should be noted that each of thedocuments placed on the document stacking tray (2) is placed so that afirst surface to be a front surface is directed upwardly and a secondsurface to be a back surface is directed downwardly.

In the vicinity of the leading end of the document stacking tray (2), aset switch (10) which functions as a sensor for detecting thepresence/absence of a document is disposed. The set switch (10) issupported above the document stacking tray (2) so as to by swingable. Inthe set switch (10), when a document is present on the document stackingtray (2), a leading end of the set switch (10) comes into contact withthe document, and moves to a retracted position (not shown) on an upperside due to the contact. On the other hand, when documents are no longerpresent on the document stacking tray (2), the leading end of the setswitch (10) moves to a position where the leading end enters a hole (notshown) formed in the document stacking tray (2). When the leading end ofthe set switch (10) moves to the position where the leading end entersthe hole, for example, the leading end of the set switch (10) interruptsan optical path of an optical sensor, and thus the fact that nodocuments are present on the document stacking tray (2) can be detected.

The document feeding portion (3) includes a pickup roller (11) disposedclose to the set switch (10), and a sheet feeding roller (12) and aseparation roller (13) disposed on a downstream side of the conveyingdirection.

The pickup roller (11) is connected to a roller drive source (not shown)such as a motor, and is rotary driven in a clockwise direction by theroller drive source to move to a position where the pickup roller (11)comes into contact with the first surface (front surface) of thedocument placed on the document stacking tray (2) (the pickup roller(11) is lowered from the position of the pickup roller (11) of FIG. 1).

The sheet feeding roller (12) is disposed so as to be held in contactwith the separation roller (13) from above the separation roller (13).The sheet feeding roller (12) is connected to a roller drive source (notshown), and is rotary driven in the clockwise direction by the rollerdrive source, thereby supplying the documents supplied from the pickuproller (11) to a downstream side one by one together with the separationroller (13). The separation roller (13) is connected to a torque limiter(not shown). In a case where one document is supplied, the separationroller (13) rotates to supply the document to the conveying portion (4),and in a case where at least two documents are supplied, the separationroller (13) stops rotating to prevent overlapped feeding.

The conveying portion (4) includes document conveying roller pairs (14)and (15), and a timing switch (16). The timing switch (16) rotates in acounterclockwise direction to move to a retracted position when theleading end of the document comes into contact with the timing switch(16), and is held at the retracted position until the documentcompletely passes the timing switch (16). Then, after the documentcompletely passes the timing switch (16), the timing switch (16) isreturned to the position illustrated in FIG. 1. The timing switch (16)is disposed so as to be associated with, for example, an optical sensor(17), and is configured in such a manner as to open an optical path ofthe optical sensor (17) when the timing switch (16) moves to theretracted position. The automatic document conveying device (1) detectsthat the leading end of the document has reached the timing switch (16)when the optical path of the optical sensor (17) is opened. On the otherhand, the automatic document conveying device (1) can detect that thedocument has passed the timing switch (16) when the optical path of theoptical sensor (17) is interrupted. Detection information of thedocument by the timing switch (16) is used for an operation timing ofeach roller, a branching member, etc. The document reading portion (18)is provided on a downstream side of the document conveying roller pair(15), for reading document information.

The discharge portion (5) includes a post-reading roller (19) and adischarge roller (20). The branching guide (6) is disposed on thedownstream side of the document conveying direction of the post-readingroller (19). The branching guide (6) is supported so as to be swingablewith respect to a swing center (6 a) in a back portion, and is biased ina direction (upward direction) opposite to the discharge portion (5) bya biasing member (not shown). Thus, the leading end of the branchingguide (6) moves up/down with respect to the swing center (6 a) in theback portion.

In the back portion (right side of FIG. 1) of the branching guide (6),the switchback portion (7) is disposed. The switchback portion (7)includes an upper switchback roller (21), a lower switchback roller(22), and a lift plate (23).

A roller drive source (not shown) is connected to the lower switchbackroller (22), and the lower switchback roller (22) can be rotary drivenin any of the clockwise and counterclockwise directions. The lift plate(23) is supported so as to be swingable with respect to a swing center(23 a) in a leading end of the lift plate (23), and the upper switchbackroller (21) is disposed in a back end thereof.

The upper switchback roller (21) is disposed so as to be held in contactwith the upper portion of the lower switchback roller (22), and iscapable of coming into contact with or being separated from the lowerswitchback roller (22) due to the swing of the lift plate (23). The liftplate (23) includes a spring (24) that is a biasing member which biasesthe lift plate (23) in a direction of bringing the upper switchbackroller (21) into contact with the lower switchback roller (22). Thus, anip between the upper switchback roller (21) and the lower switchbackroller (22) can be opened/closed.

In the automatic document conveying device (1) according to the presentinvention, the switch of a conveying path of the branching guide (6) andthe open/close of the nip between the upper switchback roller (21) andthe lower switchback roller (22) of the switchback portion (7) areperformed in one drive portion. The drive portion includes a drivesource, a drive member, and a drive transmission mechanism, and thedrive transmission mechanism includes a driven member and an operationtransmission mechanism which performs the switch operation of theconveying path by the branching guide (6) and the open/close operationof the nip of the switchback roller pair (21, 22).

According to the above-mentioned configuration, the switch of theconveying path of the branching guide and the open/close of the nip ofthe switchback roller pair are performed in one drive portion.Therefore, the setting space of the drive portion can be reduced.Further, the number of parts of the drive portion can be reduced toobtain a simple configuration, and accordingly the number of assemblysteps can be reduced, and hence a production cost can be lowered.

Hereinafter, an embodiment of the drive portion is described in detail.FIG. 2 is a perspective view illustrating the drive portion of theautomatic document conveying device (1) according to the presentinvention, FIG. 3 is a side view illustrating the drive portion of theautomatic document conveying device (1) according to the presentinvention, and FIG. 4 is an enlarged perspective view illustrating thedrive portion of the automatic document conveying device (1) accordingto the present invention. FIGS. 2 and 3 are views seen from the backside of FIG. 1.

As illustrated in FIGS. 2 and 3, a drive portion (25) includes a drivesource (26) providing a drive force, a drive gear (28) used as a drivemember fixed to the drive source (26), and a drive transmissionmechanism (27) which transmits the drive force of the drive source (26)to the branching guide (6) and the switchback roller pair (21, 22) viathe drive gear (28).

The drive transmission mechanism (27) includes driven gears (29), (30),and (31) used as driven members for transmitting a drive force from thedrive gear (28), and an operation transmission mechanism (32) whichconverts drive forces transmitted from the driven gears (29), (30), and(31) into a switch operation of the conveying path of the branchingguide (6) and an open/close operation of the nip of the switchbackroller pair (21, 22).

The operation transmission mechanism (32) includes a cam (33) whichconverts the drive forces transmitted from the driven gears (29), (30),and (31) to the switch operation of the conveying path of the branchingguide (6) and the open/close operation of the nip of the switchbackroller pair (21, 22), a position detection sensor (34) which is aposition detection member that detects a stop position (home position)of the cam (33), and an operation link (35) which is an operation memberthat transmits the operation converted by the cam (33) to the upperswitchback roller (21).

According to the above-mentioned configuration, the configuration of theautomatic document conveying device can be further simplified. Thus, thenumber of assembly steps can be reduced, which can further lower aproduction cost. Further, control between the switch of the conveyingpath by the branching guide and the open/close of the nip of theswitchback roller pair can be performed precisely. Further, the driveforce of the drive source is transmitted to the cam precisely. Further,the automatic conveyance of a document at a time of double-side printingcan be performed precisely.

The driven gear (31) is attached to a spindle (31 a) extendingsubstantially horizontally in a width direction of a document, and isrotatably provided together with the spindle (31 a). The driven gear(31) is engaged with the drive gear (28) via the driven gears (29) and(30), and the drive force of the drive source (26) is transmitted to thedriven gear (31). In the case of this embodiment, the drive source (26)includes one motor.

According to the above-mentioned configuration, with a simpleconfiguration, the switch of the conveying path of the branching guideand the open/close of the nip of the switchback roller pair can beperformed. Therefore, the setting space of the drive source can bereduced, which can lower a production cost. Further, only one motor isused as the drive source, and hence the noise from the automaticdocument conveying device can be reduced, compared with the case ofusing a solenoid, etc. as the drive source, for example.

The cam (33) is fixed to an end portion on a back surface side of thespindle (31 a) that is a rotation shaft. This allows the cam (33) torotate in a perpendicular surface with respect to an axial direction ofthe spindle, along with rotation of the driven gear (31). Further, thecam (33) includes two portions placed adjacent to each other along theaxial direction of the spindle (31 a); as illustrated in FIG. 4, and isformed of a first portion having a first circumferential surface (33 a)that is a first cam and a second portion having a second circumferentialsurface (33 b) that is a second cam. As illustrated in FIG. 4, the firstcircumferential surface (33 a) of the first portion of the cam (33) isheld in contact with a lower surface of the operation link (35), and thesecond circumferential surface (33 b) of the second portion is held incontact with a guide shaft (36) disposed above the branching guide (6)in a perpendicular direction.

According to the above-mentioned configuration, the first cam and thesecond cam are provided integrally, and hence the drive portion can bedown-sized to obtain a simple configuration.

Returning to FIGS. 2 and 3, one end portion of the operation link (35)is fixed to one end portion of a spindle (35 a) extending in asubstantially horizontal manner in the width direction of the document,and the other end portion of the spindle (35 a) is fixed to the swingcenter (23 a) of the lift plate (23) (see FIG. 1). The operation link(35) is disposed so as to be held in contact with an upper portion ofthe first circumferential surface (33 a) of the cam (33). Thus, theoperation link (35) swings following the rotation of the cam (33), andthe operation thereof is transmitted to the lift plate (23) of theswitchback portion (7) via the spindle (35 a). Thus, the upperswitchback roller (21) disposed on the lift plate (23) moves up/downabout the swing center (23 a), and thus, the open/close of the nipbetween the upper switchback roller (21) and the lower switchback roller(22) is performed.

When the branching guide (6) comes into contact with the secondcircumferential surface (33 b) of the cam (33), the branching guide (6)swings with respect to the swing center (6 a) disposed in the backportion thereof along with the movement of the cam (33). The guide shaft(36) is provided above the branching guide (6) in the perpendiculardirection from the swing center (6 a) of the branching guide (6). Theguide shaft (36) is provided with a convex portion (36 a) extendinghorizontally at an upper end portion. The convex portion (36 a) isalways held in contact with the second circumferential surface (33 b) ofthe cam (33). Thus, the branching guide (6) moves up/down its leadingend in the conveying direction of the document along with the rotationof the cam (33), and thus, switches the conveying direction of thedocument.

The position detection sensor (34) specifies the home position of thecam (33), and is formed of a photointerrupter which is an opticalsensor. The position detection sensor (34) includes a light-emittingportion and a light-receiving portion opposed to each other, and a gapis provided therebetween. The position detection sensor (34) identifieslight output from the light-emitting portion when the light-receivingportion receives the light, and hence, detects the presence of anothermember between the light-emitting portion and the light-receivingportion when the light is interrupted.

The driven gear (31) includes a shield plate (37) protruding from a partof the outer circumference of the driven gear (31), and is disposed sothat the shield plate (37) enters the gap provided in the positiondetection sensor (34). More specifically, the driven gear (31) and thecam (33) are driven together, and hence when the position of the shieldplate (37) of the driven gear (31) is detected by the position detectionsensor (34), the position of the cam (33) can also be specified.Generally, in a case where the shield plate (37) of the driven gear (31)is present in the gap of the position detection sensor (34), the cam(33) is at the home position.

According to the above-mentioned configuration, the stop position of thecam can be controlled precisely.

Due to the above-mentioned configuration, the switch of the conveyingpath of the branching guide (6) and the open/close of the nip betweenthe upper switchback roller (21) and the lower switchback roller (22)can be performed with one drive portion. In this embodiment, althoughthe drive gear and the driven gear are used as the drive member and thedriven member, the drive member and the driven member are not limitedthereto. For example, with the use of a drive pulley and a driven pulleyas the drive member and the driven member, respectively, a belt may bewound around both the pulleys so as to transmit a drive force.

The operation of the above-mentioned automatic document conveying device(1) is described with reference to the drawings. FIG. 5 is across-sectional view of the automatic document conveying deviceaccording to the embodiment of the present invention during single-sideconveyance, and FIG. 6 is a cross-sectional view of the automaticdocument conveying device according to the embodiment of the presentinvention during double-side conveyance. In the following description,for convenience, the position of the branching guide (6) illustrated inFIG. 5 is assumed to be an initial position. Arrows in the figuresindicate the conveying direction of the document.

A conveying path of a document in a case of reading only one side (firstsurface) of the document is described below in detail with reference toFIG. 5.

When documents are placed on the document stacking tray (2), the setswitch (10) is retracted upward, and thus, the preparation for conveyingthe documents is completed. Only the first surfaces of the documents areread, and hence the cam (33) is not driven from the home position.

When the automatic document conveying device (1) receives a start signalinput from an operation panel (not shown), the pickup roller (11) isrotated in the clockwise direction. Then, the pickup roller (11) islowered to a position where the pickup roller (11) comes into contactwith the documents placed on the document stacking tray (2) to supplythe document on an uppermost side to the document conveying path (38).The documents supplied from the pickup roller (11) are supplied to thedocument conveying path (38) by the separation roller (13) one by one.

When the leading end of the supplied document passes the timing switch(16), the passage of the document is detected, and the informationthereof is utilized for an operation timing of each roller, thebranching guide, etc. Then, the document is conveyed to the documentreading portion (18) by the document conveying roller pairs (14) and(15), and is discharged to the document discharge tray (8) due to therotation of the post-reading roller (19) and the discharge roller (20)in the clockwise direction.

A conveying path of a document in a case of reading both surfaces (firstand second surfaces) of the document is described below in detail withreference to FIG. 6.

When documents are placed on the document stacking tray (2), the setswitch (10) is retracted upward, and thus, the preparation for conveyingthe documents is completed.

When the automatic document conveying device (1) receives a start signalinput from the operation panel (not shown), the pickup roller (11) isrotated in the clockwise direction. Then, the pickup roller (11) islowered to a position where the pickup roller (11) comes into contactwith the documents placed on the document stacking tray (2) to supplythe document on the uppermost side to the document conveying path (38).The documents supplied from the pickup roller (11) are supplied to thedocument conveying path (38) by the separation roller (13) one by one.

When the leading end of the supplied document passes the timing switch(16), the passage of the document is detected, and the drive source (26)(see FIG. 3) starts driving. Thus, the cam (33) (see FIG. 3) startsrotating, and the branching guide (6) is disposed at a positionillustrated in FIG. 6 in accordance with the rotation of the cam (33).After the document passes through the document conveying path (38) andthe first surface thereof is read by the document reading portion (18),the document is sent to the switchback conveying path (39) by thepost-reading roller (19). The conveyed document is conveyed to theswitchback conveying path (39) due to the rotation of the lowerswitchback roller (22) in the clockwise direction, and is inverted.After being inverted, the document is sent to the document conveyingpath (38) again due to the inverse rotation of the lower switchbackroller (22) in the counterclockwise direction. The position of thebranching guide (6) at this time has returned to the home position(position of FIG. 5). This can prevent the document from being sentinversely from the switchback conveying path (39) to a documentdischarge path (40). The timing of the inversion of the document ismeasured based on the passage time of the leading end of the documentdetected by the timing switch (16).

After the document is detected by the timing switch (16) again, thesecond surface is read by the document reading portion (18). Thebranching guide (6) is disposed at the position illustrated in FIG. 6again, and the document is conveyed to the switchback conveying path(39) to be inverted. After being inverted, the document is sent to thedocument conveying path (38). However, the document is not read in thedocument reading portion (18). Next, the position of the branching guide(6) is set at the home position (position of FIG. 5). Consequently, thedocument is discharge onto the document discharge tray (8) by thepost-reading roller (19) and the discharge roller (20). The conveyanceof the document without being subjected to reading is performed so as toadjust the front and back sides of the documents.

The rotation operation of the cam at the time of reading both surfacesof the document, the branching guide, and the open/close operation stateof the nip of the switchback roller pair are described in detail withreference to FIGS. 7 to 12, and the conveying path of the document isdescribed in detail with reference to FIGS. 5 and 6.

FIG. 7 illustrates a state of the cam (33) from the start of theoperation of the automatic document conveying device (1) to the readingof the first surface of the document, and also illustrates an open/closestate of the nip of the switchback roller pair (21, 22) from the readingof the first surface of the document to the conveyance of the documentto the switchback conveying path (39). FIG. 8 illustrates a state of thecam (33) from the reading of the first surface of the document to theconveyance of the document to the switchback conveying path (39), andalso illustrates the open/close state of the nip of the switchbackroller pair (21, 22) from the reading of the first surface of thedocument to the conveyance of the document to the switchback conveyingpath (39). FIG. 9 illustrates a state of the cam (33) when the documentis conveyed from the switchback conveying path (39) to the documentconveying path (38), and also illustrates the open/close state of thenip of the switchback roller pair (21, 22) from the reading of the firstsurface of the document to the conveyance of the document to theswitchback conveying path (39). Further, FIG. 10 illustrates a state ofthe cam (33) from the reading of the second surface of the document tothe conveyance of the document to the switchback conveying path (39),and also illustrates the open/close state of the nip of the switchbackroller pair (21, 22) from the reading of the first surface of thedocument to the conveyance of the document to the switchback conveyingpath (39). FIG. 11 illustrates a state of the cam (33) when the documenthas arrived at the switchback conveying path (39), and also illustratesthe open/close state of the nip of the switchback roller pair (21, 22)from the reading of the first surface of the document to the conveyanceof the document to the switchback conveying path (39). FIG. 12illustrates a state of the cam (33) when the document is conveyed fromthe switchback conveying path (39) to the document conveying path (39),and also illustrates the open/close state of the nip of the switchbackroller pair (21, 22) from the reading of the first surface of thedocument to the conveyance of the document to the switchback conveyingpath (39). Regarding each of the cam (33) and the branching guide (6),when the cam (33) and the branching guide (6) are located at thepositions illustrated in FIG. 7, a left side thereof in the figure isassumed to be a leading end, a right side thereof in the figure isassumed to be a back end, an upper side thereof in the figure is assumedto be an upper portion, and a lower side thereof in the figure isassumed to be a lower portion. In the following description, thepositions of the cam (33), the upper switchback roller (21), and thebranching guide (6) illustrated in FIG. 7 are assumed to be respectivehome positions.

As described above, the first circumferential surface (33 a) of the cam(33) is held in contact with the operation link (35), and the secondcircumferential surface (33 b) is always held in contact with the convexportion (36 a) of the guide shaft (36) of the branching guide (6). Thus,the branching guide (6) is operated in accordance with the rotation ofthe cam (33), and the upper switchback roller (21) connected to theoperation link (35) is also operated in accordance with the rotation ofthe cam (33). Here, the direction in which the cam (33) rotates is theclockwise direction as indicated by the arrow of FIG. 7.

As illustrated in FIG. 7, during a period from the start of theoperation of the automatic document conveying device (1) to the readingof the first surface of the document, the cam (33) is not operated.Thus, the branching guide (6) and the upper switchback roller (21) areat the home positions, and the nip between the upper switchback roller(21) and the lower switchback roller (22) is closed.

FIG. 8 illustrates the operation of the cam (33) from the reading of thefirst surface of the document to the conveyance of the document to theswitchback conveying path (39). The leading end of the secondcircumferential surface (33 b) of the cam (33) pushes the convex portion(36 a) of the guide shaft (36) of the branching guide (6) to the leadingend direction. Thus, the branching guide (6) is rotated about the swingcenter (6 a) and the leading end of the branching guide (6) is pusheddownwardly. Consequently, as illustrated in FIG. 6, the documentconveying path (38) to the document discharge tray (8) is closed by thebranching guide (6), and the document is conveyed to the switchbackconveying path (39). In this case, the nip between the upper switchbackroller (21) and the lower switchback roller (22) remains in a closedstate, and hence, the conveyance of the document to the switchbackconveying path (39) due to the rotation of the lower switchback roller(22) in the clockwise direction is completed.

When the document is conveyed from the switchback conveying path (39) tothe document conveying path (38), as illustrated in FIG. 9, the cam (33)is rotated in the clockwise direction, and the convex portion (36 a) ofthe guide shaft (36) of the branching guide comes into contact with aconcave portion in the lower portion formed between the leading end andthe back end of the circumferential surface (33 b) of the second surfaceof the cam (33). Thus, the leading end of the branching guide (6) ispushed up, and the branching guide (6) returns to the initial position.This allows the state illustrated in FIG. 5 to be obtained, and thedocument is prevented from being sent inversely from the switchbackconveying path (39) to the document discharge path (40) and is conveyedto the document conveying path (39) precisely.

When the document is conveyed to the document conveying path (38), andthe leading end thereof reaches the nip of the document conveying rollerpair (14) (see FIG. 6), as illustrated in FIG. 10, the cam (33) isfurther rotated, and the leading end of the first circumferentialsurface (33 a) of the cam (33) comes into contact with the operationlink (35). The operation link (35) is connected to the swing center (23a) of the lift plate (23) (see FIG. 2) of the switchback portion (7) viathe spindle (35 a). Thus, the lift plate (23) is pushed upwardly withrespect to the swing center (23 a) of the leading end. Thus, the upperswitchback roller (21) is pushed up, and the upper switchback roller(21) and the lower switchback roller (22) are separated from each other.Further, the back end of the second circumferential surface (33 b) ofthe cam (33) pushes the convex portion (36 a) of the guide shaft (36) ofthe branching guide (6), and the leading end of the branching guide (6)is pushed downwardly with respect to the swing center (6 a). Thus, thedocument is supplied to the switchback conveying path (39) after thesecond surface is read.

According to the above-mentioned configuration, even if the switchbackroller pair is separately disposed from the branching guide, theconversion operation of the second cam is transmitted by the operationlink that is an operation member. Therefore, the first and second camsmay be provided integrally to obtain a simple configuration.

There is a time period when the conveying directions become oppositebetween the leading end and the back end of a document, and hence it isnecessary to open the nip of the switchback roller pair (21, 22).Specifically, in a case where the length of the document is equal to ormore than a predetermined length, there is a case where the leading endof the document has reached the switchback conveying path (39), whereasthe back end of the document still remains in the switchback conveyingpath (39), during reading of the second surface. In this case, it isnecessary to convey the leading end of the document in the rightdirection of the switchback roller pair (21, 22), whereas it isnecessary to convey the back end of the document in the left directionof the switchback roller pair (21, 22), i.e., in the document conveyingpath (38) direction. Thus, the conveying directions become oppositebetween the leading end and the back end of the document, which makes itimpossible to convey the document by the switchback roller pair (21,22). Therefore, it is necessary to open the nip of the switchback rollerpair (21, 22).

When the document reaches the switchback conveying path (39), asillustrated in FIG. 11, the cam (33) is further rotated, and the lowerportion of the first circumferential surface (33 a) of the cam (33)comes into contact with the operation link (35). Thus, the lift plate(23) of the switchback portion (7) is pushed down through the force ofthe spring (24) with respect to the swing center (23 a) of the leadingend of the lift plate (23), and the upper switchback roller (21)provided at the back end of the lift plate (23) comes into contact withthe lower switchback roller (22). At this time, the back end of thesecond circumferential surface (33 b) of the cam (33) still remains incontact with the convex portion (36 a) of the guide shaft (36) of thebranching guide (6). Therefore, the leading end of the branching guide(6) remains in a pushed-down state.

When the document is conveyed again from the switchback conveying path(39) to the document conveying path (38), as illustrated in FIG. 12, thecam (33) is further rotated in the clockwise direction, and the convexportion (36 a) of the guide shaft (36) of the branching guide comes intocontact with a concave portion in the upper portion of the secondcircumferential surface (33 b) of the cam (33). Thus, the leading end ofthe branching guide (6) is pushed upwardly and the branching guide (6)returns to the initial position. Thus, the document is prevented frombeing conveyed inversely from the switchback conveying path (39) to thedocument discharge path (40) and is conveyed to the document conveyingpath (38) precisely.

Next, the document is conveyed through the document conveying path (38)to the document reading portion (18). Then, the conveyance of thedocument without being subjected to the reading is performed by thepost-reading roller (19) and the discharge roller (20), and isdischarged onto the document discharge tray (8). At this time, the cam(33) is rotated once, and the cam (33) and the branching guide (6)return to the home positions illustrated in FIG. 7.

When the document is conveyed by the automatic document conveying device(1) described above, and when the image data on the document is read bythe document reading portion (18), a toner image is formed on the sheetbased on the image data on the document by an electrophotographicprocess in the image forming apparatus including the automatic documentconveying device (1).

According to the above-mentioned configuration, there can be provided animage forming apparatus including an automatic document conveyingdevice, which is capable of reducing the number of drive sources such asa motor, down-sizing of the drive portion, reducing the number of partsof the drive portion to obtain a simple configuration, and further,capable of suppressing an operation sound to reduce noise.

The automatic document conveying device and the image forming apparatusincluding the same according to the present invention can be utilizedpreferably in various copiers, printers, and facsimiles.

1-10. (canceled)
 11. An automatic document conveying device, comprising:a document feeding portion that feeds a document from a documentstacking tray; a conveying portion that conveys the document which isfed, to a document reading portion; a discharge portion that dischargesthe document after being read to a discharge tray; a branching guidethat switches a conveying path so that a second surface is read afterthe first surface of the document is read; a contact portion that isprovided on the branching guide; a switchback roller pair for sendingthe document to the conveying portion again after the conveying path isswitched by the branching guide; a biasing member that biases theswitchback roller pair in a direction of bringing the switchback rollerpair into mutual contact; a lift member that swings to bring theswitchback roller pair out of mutual contact; one drive source thatprovides a drive force; a drive member that is fixed to the drivesource; a driven member that transmits the drive force from the drivemember; a cam that is moved by the driven member; a shield plate that isdisposed coaxially with the cam and that is driven together with thecam; and a position detection sensor that detects a position of theshield plate, wherein the cam comprises: a first cam that is moved bythe driven member so as to rotate the lift member in a direction ofbringing the switchback roller pair out of mutual contact against abiasing force of the biasing member; and a second cam that makes contactwith the contact portion and that, by being moved by the driven member,makes the contact portion swing so that, as the contact portion swings,the conveying path of the branching guide is switched, and wherein thefirst and second cams are disposed coaxially with each other.
 12. Theautomatic document conveying device according to claim 11, wherein anoperation of reading both surfaces of the document can be completed byrotating the cam once from a home position to make it return to the homeposition.
 13. The automatic document conveying device according to claim11, wherein the drive source includes one motor.
 14. The automaticdocument conveying device according to claim 11, wherein each of thedrive member and the driven member comprises a gear.
 15. An imageforming apparatus comprising the automatic document conveying deviceaccording to claim 11.